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<link rel="import" href="../polymer/polymer.html">

<script>
  (function() {
  'use strict';

  /**
   * Chrome uses an older version of DOM Level 3 Keyboard Events
   *
   * Most keys are labeled as text, but some are Unicode codepoints.
   * Values taken from:
   * http://www.w3.org/TR/2007/WD-DOM-Level-3-Events-20071221/keyset.html#KeySet-Set
   */
  var KEY_IDENTIFIER = {
    'U+0008': 'backspace',
    'U+0009': 'tab',
    'U+001B': 'esc',
    'U+0020': 'space',
    'U+007F': 'del'
  };

  /**
   * Special table for KeyboardEvent.keyCode.
   * KeyboardEvent.keyIdentifier is better, and KeyBoardEvent.key is even better
   * than that.
   *
   * Values from:
   * https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent.keyCode#Value_of_keyCode
   */
  var KEY_CODE = {
    8: 'backspace',
    9: 'tab',
    13: 'enter',
    27: 'esc',
    33: 'pageup',
    34: 'pagedown',
    35: 'end',
    36: 'home',
    32: 'space',
    37: 'left',
    38: 'up',
    39: 'right',
    40: 'down',
    46: 'del',
    106: '*'
  };

  /**
   * MODIFIER_KEYS maps the short name for modifier keys used in a key
   * combo string to the property name that references those same keys
   * in a KeyboardEvent instance.
   */
  var MODIFIER_KEYS = {
    'shift': 'shiftKey',
    'ctrl': 'ctrlKey',
    'alt': 'altKey',
    'meta': 'metaKey'
  };

  /**
   * KeyboardEvent.key is mostly represented by printable character made by
   * the keyboard, with unprintable keys labeled nicely.
   *
   * However, on OS X, Alt+char can make a Unicode character that follows an
   * Apple-specific mapping. In this case, we fall back to .keyCode.
   */
  var KEY_CHAR = /[a-z0-9*]/;

  /**
   * Matches a keyIdentifier string.
   */
  var IDENT_CHAR = /U\+/;

  /**
   * Matches arrow keys in Gecko 27.0+
   */
  var ARROW_KEY = /^arrow/;

  /**
   * Matches space keys everywhere (notably including IE10's exceptional name
   * `spacebar`).
   */
  var SPACE_KEY = /^space(bar)?/;

  /**
   * Matches ESC key.
   *
   * Value from: http://w3c.github.io/uievents-key/#key-Escape
   */
  var ESC_KEY = /^escape$/;

  /**
   * Transforms the key.
   * @param {string} key The KeyBoardEvent.key
   * @param {Boolean} [noSpecialChars] Limits the transformation to
   * alpha-numeric characters.
   */
  function transformKey(key, noSpecialChars) {
    var validKey = '';
    if (key) {
      var lKey = key.toLowerCase();
      if (lKey === ' ' || SPACE_KEY.test(lKey)) {
        validKey = 'space';
      } else if (ESC_KEY.test(lKey)) {
        validKey = 'esc';
      } else if (lKey.length == 1) {
        if (!noSpecialChars || KEY_CHAR.test(lKey)) {
          validKey = lKey;
        }
      } else if (ARROW_KEY.test(lKey)) {
        validKey = lKey.replace('arrow', '');
      } else if (lKey == 'multiply') {
        // numpad '*' can map to Multiply on IE/Windows
        validKey = '*';
      } else {
        validKey = lKey;
      }
    }
    return validKey;
  }

  function transformKeyIdentifier(keyIdent) {
    var validKey = '';
    if (keyIdent) {
      if (keyIdent in KEY_IDENTIFIER) {
        validKey = KEY_IDENTIFIER[keyIdent];
      } else if (IDENT_CHAR.test(keyIdent)) {
        keyIdent = parseInt(keyIdent.replace('U+', '0x'), 16);
        validKey = String.fromCharCode(keyIdent).toLowerCase();
      } else {
        validKey = keyIdent.toLowerCase();
      }
    }
    return validKey;
  }

  function transformKeyCode(keyCode) {
    var validKey = '';
    if (Number(keyCode)) {
      if (keyCode >= 65 && keyCode <= 90) {
        // ascii a-z
        // lowercase is 32 offset from uppercase
        validKey = String.fromCharCode(32 + keyCode);
      } else if (keyCode >= 112 && keyCode <= 123) {
        // function keys f1-f12
        validKey = 'f' + (keyCode - 112 + 1);
      } else if (keyCode >= 48 && keyCode <= 57) {
        // top 0-9 keys
        validKey = String(keyCode - 48);
      } else if (keyCode >= 96 && keyCode <= 105) {
        // num pad 0-9
        validKey = String(keyCode - 96);
      } else {
        validKey = KEY_CODE[keyCode];
      }
    }
    return validKey;
  }

  /**
   * Calculates the normalized key for a KeyboardEvent.
   * @param {KeyboardEvent} keyEvent
   * @param {Boolean} [noSpecialChars] Set to true to limit keyEvent.key
   * transformation to alpha-numeric chars. This is useful with key
   * combinations like shift + 2, which on FF for MacOS produces
   * keyEvent.key = @
   * To get 2 returned, set noSpecialChars = true
   * To get @ returned, set noSpecialChars = false
   */
  function normalizedKeyForEvent(keyEvent, noSpecialChars) {
    // Fall back from .key, to .detail.key for artifical keyboard events,
    // and then to deprecated .keyIdentifier and .keyCode.
    if (keyEvent.key) {
      return transformKey(keyEvent.key, noSpecialChars);
    }
    if (keyEvent.detail && keyEvent.detail.key) {
      return transformKey(keyEvent.detail.key, noSpecialChars);
    }
    return transformKeyIdentifier(keyEvent.keyIdentifier) ||
        transformKeyCode(keyEvent.keyCode) || '';
  }

  function keyComboMatchesEvent(keyCombo, event) {
    // For combos with modifiers we support only alpha-numeric keys
    var keyEvent = normalizedKeyForEvent(event, keyCombo.hasModifiers);
    return keyEvent === keyCombo.key &&
        (!keyCombo.hasModifiers ||
         (!!event.shiftKey === !!keyCombo.shiftKey &&
          !!event.ctrlKey === !!keyCombo.ctrlKey &&
          !!event.altKey === !!keyCombo.altKey &&
          !!event.metaKey === !!keyCombo.metaKey));
  }

  function parseKeyComboString(keyComboString) {
    if (keyComboString.length === 1) {
      return {combo: keyComboString, key: keyComboString, event: 'keydown'};
    }
    return keyComboString.split('+')
        .reduce(function(parsedKeyCombo, keyComboPart) {
          var eventParts = keyComboPart.split(':');
          var keyName = eventParts[0];
          var event = eventParts[1];

          if (keyName in MODIFIER_KEYS) {
            parsedKeyCombo[MODIFIER_KEYS[keyName]] = true;
            parsedKeyCombo.hasModifiers = true;
          } else {
            parsedKeyCombo.key = keyName;
            parsedKeyCombo.event = event || 'keydown';
          }

          return parsedKeyCombo;
        }, {combo: keyComboString.split(':').shift()});
  }

  function parseEventString(eventString) {
    return eventString.trim().split(' ').map(function(keyComboString) {
      return parseKeyComboString(keyComboString);
    });
  }

  /**
   * `Polymer.IronA11yKeysBehavior` provides a normalized interface for processing
   * keyboard commands that pertain to [WAI-ARIA best
   * practices](http://www.w3.org/TR/wai-aria-practices/#kbd_general_binding). The
   * element takes care of browser differences with respect to Keyboard events and
   * uses an expressive syntax to filter key presses.
   *
   * Use the `keyBindings` prototype property to express what combination of keys
   * will trigger the callback. A key binding has the format
   * `"KEY+MODIFIER:EVENT": "callback"` (`"KEY": "callback"` or
   * `"KEY:EVENT": "callback"` are valid as well). Some examples:
   *
   *      keyBindings: {
   *        'space': '_onKeydown', // same as 'space:keydown'
   *        'shift+tab': '_onKeydown',
   *        'enter:keypress': '_onKeypress',
   *        'esc:keyup': '_onKeyup'
   *      }
   *
   * The callback will receive with an event containing the following information
   * in `event.detail`:
   *
   *      _onKeydown: function(event) {
   *        console.log(event.detail.combo); // KEY+MODIFIER, e.g. "shift+tab"
   *        console.log(event.detail.key); // KEY only, e.g. "tab"
   *        console.log(event.detail.event); // EVENT, e.g. "keydown"
   *        console.log(event.detail.keyboardEvent); // the original KeyboardEvent
   *      }
   *
   * Use the `keyEventTarget` attribute to set up event handlers on a specific
   * node.
   *
   * See the [demo source
   * code](https://github.com/PolymerElements/iron-a11y-keys-behavior/blob/master/demo/x-key-aware.html)
   * for an example.
   *
   * @demo demo/index.html
   * @polymerBehavior
   */
  Polymer.IronA11yKeysBehavior = {
    properties: {
      /**
       * The EventTarget that will be firing relevant KeyboardEvents. Set it to
       * `null` to disable the listeners.
       * @type {?EventTarget}
       */
      keyEventTarget: {
        type: Object,
        value: function() {
          return this;
        }
      },

      /**
       * If true, this property will cause the implementing element to
       * automatically stop propagation on any handled KeyboardEvents.
       */
      stopKeyboardEventPropagation: {type: Boolean, value: false},

      _boundKeyHandlers: {
        type: Array,
        value: function() {
          return [];
        }
      },

      // We use this due to a limitation in IE10 where instances will have
      // own properties of everything on the "prototype".
      _imperativeKeyBindings: {
        type: Object,
        value: function() {
          return {};
        }
      }
    },

    observers: ['_resetKeyEventListeners(keyEventTarget, _boundKeyHandlers)'],


    /**
     * To be used to express what combination of keys  will trigger the relative
     * callback. e.g. `keyBindings: { 'esc': '_onEscPressed'}`
     * @type {!Object}
     */
    keyBindings: {},

    registered: function() {
      this._prepKeyBindings();
    },

    attached: function() {
      this._listenKeyEventListeners();
    },

    detached: function() {
      this._unlistenKeyEventListeners();
    },

    /**
     * Can be used to imperatively add a key binding to the implementing
     * element. This is the imperative equivalent of declaring a keybinding
     * in the `keyBindings` prototype property.
     *
     * @param {string} eventString
     * @param {string} handlerName
     */
    addOwnKeyBinding: function(eventString, handlerName) {
      this._imperativeKeyBindings[eventString] = handlerName;
      this._prepKeyBindings();
      this._resetKeyEventListeners();
    },

    /**
     * When called, will remove all imperatively-added key bindings.
     */
    removeOwnKeyBindings: function() {
      this._imperativeKeyBindings = {};
      this._prepKeyBindings();
      this._resetKeyEventListeners();
    },

    /**
     * Returns true if a keyboard event matches `eventString`.
     *
     * @param {KeyboardEvent} event
     * @param {string} eventString
     * @return {boolean}
     */
    keyboardEventMatchesKeys: function(event, eventString) {
      var keyCombos = parseEventString(eventString);
      for (var i = 0; i < keyCombos.length; ++i) {
        if (keyComboMatchesEvent(keyCombos[i], event)) {
          return true;
        }
      }
      return false;
    },

    _collectKeyBindings: function() {
      var keyBindings = this.behaviors.map(function(behavior) {
        return behavior.keyBindings;
      });

      if (keyBindings.indexOf(this.keyBindings) === -1) {
        keyBindings.push(this.keyBindings);
      }

      return keyBindings;
    },

    _prepKeyBindings: function() {
      this._keyBindings = {};

      this._collectKeyBindings().forEach(function(keyBindings) {
        for (var eventString in keyBindings) {
          this._addKeyBinding(eventString, keyBindings[eventString]);
        }
      }, this);

      for (var eventString in this._imperativeKeyBindings) {
        this._addKeyBinding(
            eventString, this._imperativeKeyBindings[eventString]);
      }

      // Give precedence to combos with modifiers to be checked first.
      for (var eventName in this._keyBindings) {
        this._keyBindings[eventName].sort(function(kb1, kb2) {
          var b1 = kb1[0].hasModifiers;
          var b2 = kb2[0].hasModifiers;
          return (b1 === b2) ? 0 : b1 ? -1 : 1;
        })
      }
    },

    _addKeyBinding: function(eventString, handlerName) {
      parseEventString(eventString).forEach(function(keyCombo) {
        this._keyBindings[keyCombo.event] =
            this._keyBindings[keyCombo.event] || [];

        this._keyBindings[keyCombo.event].push([keyCombo, handlerName]);
      }, this);
    },

    _resetKeyEventListeners: function() {
      this._unlistenKeyEventListeners();

      if (this.isAttached) {
        this._listenKeyEventListeners();
      }
    },

    _listenKeyEventListeners: function() {
      if (!this.keyEventTarget) {
        return;
      }
      Object.keys(this._keyBindings).forEach(function(eventName) {
        var keyBindings = this._keyBindings[eventName];
        var boundKeyHandler = this._onKeyBindingEvent.bind(this, keyBindings);

        this._boundKeyHandlers.push(
            [this.keyEventTarget, eventName, boundKeyHandler]);

        this.keyEventTarget.addEventListener(eventName, boundKeyHandler);
      }, this);
    },

    _unlistenKeyEventListeners: function() {
      var keyHandlerTuple;
      var keyEventTarget;
      var eventName;
      var boundKeyHandler;

      while (this._boundKeyHandlers.length) {
        // My kingdom for block-scope binding and destructuring assignment..
        keyHandlerTuple = this._boundKeyHandlers.pop();
        keyEventTarget = keyHandlerTuple[0];
        eventName = keyHandlerTuple[1];
        boundKeyHandler = keyHandlerTuple[2];

        keyEventTarget.removeEventListener(eventName, boundKeyHandler);
      }
    },

    _onKeyBindingEvent: function(keyBindings, event) {
      if (this.stopKeyboardEventPropagation) {
        event.stopPropagation();
      }

      // if event has been already prevented, don't do anything
      if (event.defaultPrevented) {
        return;
      }

      for (var i = 0; i < keyBindings.length; i++) {
        var keyCombo = keyBindings[i][0];
        var handlerName = keyBindings[i][1];
        if (keyComboMatchesEvent(keyCombo, event)) {
          this._triggerKeyHandler(keyCombo, handlerName, event);
          // exit the loop if eventDefault was prevented
          if (event.defaultPrevented) {
            return;
          }
        }
      }
    },

    _triggerKeyHandler: function(keyCombo, handlerName, keyboardEvent) {
      var detail = Object.create(keyCombo);
      detail.keyboardEvent = keyboardEvent;
      var event =
          new CustomEvent(keyCombo.event, {detail: detail, cancelable: true});
      this[handlerName].call(this, event);
      if (event.defaultPrevented) {
        keyboardEvent.preventDefault();
      }
    }
  };
  })();
</script>
